Magic Monday Journal Club

20th January 2014

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A journal club very.... bald. Those who attended will understand..



The Effect of Gravitational Focusing on Annual Modulation

by S. K. Lee, M. Lisanti, A. H. G. Peter, B. R. Safdi


This paper is about the impact of  gravitational focusing on dark matter direct detection experiments.  Dark matter particles are focused by the gravitational potential of the Sun which changes their velocity distribution and thus affects the direct detetcion rate.  Although the effect on the total  rate is negligible, it can have a significant effect on the annual modulation.  This is due to the fact that gravitational focusing also modulates with a 1-year phase but has a maximum around March 1 (rather than June 1, as for the standard annual modulation), thus the maximum of the direct detection rate can be shifted from June toward March.  On one hand, gravitational focusing gives more freedom in interpreting the annual modulation signal of experiments like DAMA and CoGeNT, which is bad.  On the other hand, it depends significantly on dark matter masses, velocity distribution, recoil energy, etc.  Thus it will provide more handles for studying dark matter properties once the signal is established, which is good.  




Search for An Annual Modulation in Three Years of CoGeNT Dark Matter Detector Data

by CoGeNT collaboration


I know what the skeptics  will tell: they will go to page 6 of the paper and read the number which is not given in the abstract (as CoGeNT guys wanted us to read at  least all the abstract) : 2.2σ. A particle guy from ATLAS will laugh, another one from LEP will ask if there is a mistake on the place of the coma.. In any case, few will take the courage to read their detailed analysis. Nevertheless, I tried. After some technical details to justify the points selected for their analysis, the authors divided their study into 4 regions: very low energy of recoils (0.5-2 keVee) and low one (2.0-4.5 keVee) and signals from de bulk compare to surface ones (distinguished by the difference in the rise time signal). A 8-10 GeV candidate should give modulation signal only from the bulk in the very low energy region, and this is what seems to be observed (se their Fig.5) as in the 3 other regions «the best fitted T [period] ... appear at random values» (first paragraph of page 4). Unfortunately such a signal has an amplitude larger that what expected (6.8 times more). The only way to escape such troubles is to suppose a non-Maxwellian distribution as low mass DM are very sensitive to high velocities queue in the distribution (kinetic energy). Applying such modification to DAMA result, DAMA region fits with CoGeNT one (their Fig. 8). However. Not any word about XENON and LUX result which clearly exclude this possibility as you can see on this same figure. The hurry guy can find an annotated version of the paper here.





Big Bang nucleosynthesis in visible and hidden-mirror sectors

by P. Ciarcelluti


The author decided to study in detail the nucleosynthesis of the mirror world and its influence on the nucleosynthesis of the visible one. The main point to understand is that through its new degrees of freedom, a dark (or mirror) universe even if coupling only gravitationally with our visible world, has an influence on primordial process through its influence on the entropy and radiation density (and then Hubble parameter). The primordial nuclear reactions are then modified and, depending on the temperature T’ of the mirror thermal bath, the abundance of each elements (Helium, deuterium) can be affected. This is nicely summarized on the Fig.1. We notice that the Lithium 7 abundance can reach lower values than the Standard one, and can alleviate the Lithium 7 abundance problem. The author then look at the mirror abundances in Fig.2, and remarks that it is quite different than the one of the visible sector. Indeed, the helium abundance can reach 80% (25% in visible world). For some details concerning the computation of Neff in such models, especially the equations (2) and (3) I added a section «dark radiation» p.63-66 in the book «Dark Matter and Physics beyond Standard Model». People interested in mirror dark matter, and more specially its influence in primordial Universe should also read «The Early Mirror Universe: Inflation, Baryogenesis, Nucleosynthesis and Dark Matter»  by Berezhiani et al.,  and also a recent review by R. Foot «Mirror dark matter: Cosmology, galaxy structure and direct detection». You can find an annoted version of the paper here.






Antihelium from Dark Matter

by E. Carlson, A. Coogan, T. Linden, S. Profumo, A. Ibarra, S. Wild



Looking for anti-helium receive a lot of interest recently. The authors tried to see if it would be possible to detect anti-helium from dark matter annihilation. Their main motivation is the suppression of background, as anti-helium flux produced by spalliation in cosmic rays is largely suppressed below 1 GeV.  All is summarized in Fig.4. So jump there and have a look: no hope to see anything. except in a very very optimistic GAPS satellite experiment.   You can find an annotated version of the paper here.




Results on neutrinoless double beta decay from GERDA Phase I

by C. Macolino on behalf of GERDA collaboration


This is a summary of the last year's results from the GERDA experiment http://arxiv.org/abs/arXiv:1307.4720 .  GERDA searched for the neutrinoless double beta decay of Germanium-76 and set the limit on the half-life at 2.1  x 10^25 years.  This translates into a limit on the effective Majorana mass around 0.3 eV, thus approaching the interesting range suggested by oscillation experiments.  





On the quantum mechanics of collision

by M. Born

1926


This is considered as the first article on interpretation of quantum mechanics. Indeed, it is in this work that the genius Born compute the amplitude of interaction of an electron hitting an atoms, proposing that the amplitude squared can be regarded as a «probability». He adds in the paper «I myself am inclined to give up determinism in the world of atoms. But that is a philosophical question for which physical arguments alone are not decisive». You can find an annotated version of this really nice paper here.




PAPER OF THE WEEK!!